Hydrodeoxygenation of waste fats and oils is a viable method for producing renewable diesel oil. In this study a model feed consisting of oleic acid and tripalmitin in molar ratio 1: 3 was hydrotreated at 325 degrees C with 20 bars H(2) in a stirred batch autoclave with a 5 wt% Pt/gamma-Al(2)O(3) catalyst, and samples were extracted periodically and analyzed on GC. Despite the significant hydrogen pressure hydrogenation of both reactants were limited and decarboxylation or decarbonylation of the ester and carboxylic acid functionalities were highly favored, yielding carbon chain lengths of odd numbers. Moreover, Pd/gamma-Al(2)O(3) was observed to be slightly more active than Pt/gamma-Al(2)O(3) and had a higher ratio of decarboxylation and decarbonylation to hydrogenation, while Ni/gamma-Al(2)O(3) was substantially less active than Pt and also showed a markedly lower ratio of decarboxylation and decarbonylation to hydrogenation. Variation of the temperature showed that triglycerides as well as free fatty acids were converted at all investigated temperatures, but the conversion of oleic acid increased from 6% to 100% when the temperature was increased from 250 degrees C to 325 degrees C. The tripalmitin reacted via a palmitic acid intermediate, and its conversion was limited by formation of this free fatty acid. (C) 2011 Elsevier Ltd. All rights reserved.